fix(mcp): clean up disconnected editor bridges

[DavidBabinec]

What changed

• clean up MCP editor bridges when Bun cancels a disconnected response stream, as well as on request aborts and failed writes
• prevent calls against destroyed bridges from creating orphan 90-second waiters
• re-resolve the active Content bridge after asynchronous authorization
• cover consumer cancellation, superseded workspaces, and post-destroy calls

Why

Repeated browser contexts could leave bridge heartbeats and responses alive because transport cancellation does not necessarily abort the server request. Over a full E2E run those leaked connections eventually made CMS API requests hang.

Verification

• bun test — 6,209 pass, 1 skip, 0 fail
• focused MCP/bridge tests — 18 pass, 0 fail
• bun run lint
• bunx tsc --noEmit
• bun run build